System and method for measuring a position of a moving object with a hybrid navigation apparatus

Abstract

A system and method for measuring a position of a moving object such as a vehicle using a hybrid-type navigation apparatus. In the system and method, at least two measurement results of an electromagnetic wave position measuring apparatus (such as a GPS position measuring apparatus) are evaluated to determine whether they are reliable with respect to the those derived by an integration calculation position measuring apparatus incorporated in the system together with the electromagnetic wave position measuring apparatus on the basis of the corresponding measurement results by means of the integration calculation position measuring apparatus. When they are determined to be highly reliable, a measurement result of the electromagnetic wave position measuring apparatus subsequent to those evaluated is set to a reference position on the basis of which the integration calculation position measuring apparatus measures the position of the moving object. Consequently, a highly reliable measurement of the position of the moving object can always be achieved.

What is claimed is: 
     
       1. A hybrid system for deriving a position of a moving object, comprising: (a) first means for receiving an electromagnetic wave from at least one satellite and a Global Positioning System for the measurement of an absolute position of the moving object and for deriving the position of the moving object on the basis of data from the received electromagnetic wave;   (b) second means, having a first sensor for detecting a movement direction of the moving object and a second sensor for detecting a movement speed of the moving object, for calculating a product of the detected movement direction and movement speed of the moving object and integrating the product with respect to time so as to derive a movement distance of the moving object and direction thereof with respect to a reference position and for calculating a sum of (i) the derived movement distance, and   (ii) direction and the reference position so as to derive a current position of the moving object;     (c) third means for comparing at least two successively derived positions of the first means with the derived current position of the second means so as to evaluate a reliability of the at least two derived positions of the first means; and   (d) fourth means for setting a latter one of said at least two derived positions of the third means as the reference position when the third means evaluates that the two derived positions of the first means are reliable.   
     
     
       2. The system according to claim 1, which further comprises means for calculating a Dilution of Precision (DOP) value of the derived position of the moving object outputted by the first means and means for evaluating the reliability of each derived position of the first means on the basis of whether the DOP value calculated by the means for calculating a DOP value is equal to or less than a predetermined value. 
     
     
       3. The system according to claim 1, which further comprises means for measuring an intensity of the received electromagnetic wave and means for evaluating the reliability of each measurement result of the first means by determining whether the measured intensity is equal to or higher than a predetermined value. 
     
     
       4. The system according to claim 1, which further comprises means for measuring a processing interval of time at which the first means measures the position of the moving object and means for evaluating the reliability of each measurement result of the first means by determining whether the processing interval of time is substantially five seconds. 
     
     
       5. The system according to claim 1, wherein the third means evaluates the reliability of each of two derived positions of the first means by comparing a distance between two derived position points derived by the first means to the distance between two points calculated by the second means and determines that the derived positions of the first means are reliable when a difference between the distances is shorter than a predetermined distance. 
     
     
       6. The system according to claim 1, wherein the third means evaluates the reliability of each of the two derived positions of the first means by comparing a direction of straight line connecting points of position derived by the first means to that calculated by the second means and evaluates that the derived positions of the first means are reliable when an angle at which both straight lines intersect is smaller than a predetermined angle. 
     
     
       7. The system according to claim 5, wherein the third means evaluates the reliability of the two derived positions of the first means by comparing a distance between two points of position derived by the first means to that calculated by the second means and evaluates that the derived positions of the first means are reliable when a difference between the distances is shorter than a predetermined distance. 
     
     
       8. The system according to claim 5, wherein the predetermined distance is 40 meters. 
     
     
       9. The system according to claim 6, wherein the predetermined angle is five degrees. 
     
     
       10. The system according to claim 1, wherein the positions of both first and second means are those respectively derived and calculated at the present time and a preceding time. 
     
     
       11. The system according to claim 1, wherein the positions of both first and second means are those respectively derived and calculated at the present time and a time preceding a preceding time. 
     
     
       12. The system according to claim 1, further including means for controlling sequential outputting of calculated positions of the second means as the positions of the moving object when the two derived positions of the first means are not reliable. 
     
     
       13. A position determining system for a vehicle, comprising: (a) first means for receiving an electromagnetic wave and deriving the position of the vehicle on the basis of the received electromagnetic wave;   (b) second means for calculating the position of the vehicle with respect to a reference position on the basis of an integration of a product of a moving direction and speed of the vehicle with respect to time, the reference position being calculated from the position of the vehicle derived by the first means;   (c) third means for evaluating the reliability of each derived position of the first means by comparing each calculated position of the second means with the corresponding derived position of said first means and setting, as a reference position in the second means, one of the derived positions subsequent to at least two consecutive derived positions of the first means which are evaluated to be reliable; and   (d) fourth means for outputting the derived position of the first means, subsequent to the two derived positions of the first means evaluated as being reliable, as the position data of the vehicle.   
     
     
       14. A method for deriving a position of a moving object, comprising the steps of: (a) deriving the position of the moving object using an electromagnetic wave position measuring apparatus;   (b) calculating the position of the moving object using an integration calculating apparatus in which the position of the moving object is derived by the sum of (i) a calculated distance and direction of the moving object, and   (ii) a reference position, the calculated distance and direction of the moving object being calculated by integrating a product, over time, of the movement direction and movement speed of the moving object;     (c) evaluating a reliability of at least two derived positions of said deriving step on the basis of comparing the calculated positions of the integration calculating apparatus corresponding to positions derived by the electromagnetic wave position measuring apparatus; and   (d) setting the derived position of the electromagnetic wave position measuring apparatus subsequent to the derived positions of the electromagnetic wave position measuring apparatus evaluated in the step (c) as a reference position when the derived positions of the electromagnetic wave position measuring apparatus are evaluated as being reliable.